This invention is concerned with a folding machine comprising folding instrumentatlities for folding the edge of a workpiece fed therepast, workpiece feeding means by which a workpiece can be fed in a succession of feed steps to move the edge of the workpiece past the folding instrumentatlities, feed speed control means for controlling the speed at which the workpiece feeding means is caused to operate, feed length control means for controlling the length of each feed step of the workpiece feeding means, and workpiece sensing means by which, as a workpiece is fed as aforesaid, an "outside" corner (as herein defined) of the edge thereof approaching the folding instrumentalities is sensed, in response to which sensing the feed length control means is actuated to reduce the feed length independently of the speed at which the workpiece feeding means is operating the feedlength control means being thereafter de-actuated in response to said sensing means no longer sensing such "outside" corner.
The term ""outside" corner" where used herein with reference to a workpiece edge is intended to indicate a portion of the edge which is curved, wherein the radius passes through the area of the workpiece, while the term ""inside" corner", where used herein in relation to a workpiece edge, is intended to indicate a portion of the edge which is curved, the radius of curvature extending away from the workpiece. As is well-known, in folding an "outside" corner, because the area of the material to be folded over exceeds the area of material onto which it is folded, customarily pleating of the folded over portion takes place, while, in the case of an "inside" corner, because the area of the material to be folded over is less than that of the material onto which it is folded, the material to be folded over is snipped.
Conventionally, in such machines, the workpiece sensing means, which may be in the form of an emitter and sensor, e.g. an infra-red emitter and a corresponding receiver, customarily forms part of a number of workpiece sensing means by which also other functions of the machine can be controlled, e.g. adhesive "on" and "off", and these sensing means are usually arranged in an array "upstream" of the folding instrumentalities of the machine, each sensing means being actuated by sensing the position of a workpiece edge in relation thereto.
The positioning of the workpiece sensing means for sensing the approach of an "outside" corner is customarily determined so as to cause pleating to be initiated just before such corner arrives at the folding instrumentalities. In this way, the operator is able to steer the corner past the folding instrumentalities at a reduced feed rate, because of the reduced feed length.
In positioning the workpiece sensing means appropriately for initiating the pleating at the desired region of the workpiece edge, however, in some instances this may mean that, since the same workpiece sensing means is used for de-actuating the feed length control means, the pleating operation is curtailed before the corner has been fully moved past the folding instrumentalities.
In order to overcome this problem, in some machines the positioning of the workpiece sensing means is therefore a compromise between the requirements for actuation and those for de-actuation of the feed length control means.